The prostate gland, which is found exclusively in male mammals, produces several components of semen and blood and several regulatory peptides. The prostate gland comprises stromal and epithelial cells, the latter group consisting of columnar secretory cells and basal nonsecretory cells. A proliferation of these basal cells as well as stromal cells gives rise to benign prostatic hyperplasia (BPH), which is one common prostate disease. Another common prostate disease is prostatic adenocarcinoma (CaP), which is the most common of the fatal pathophysiological prostate cancers, and involves a malignant transformation of epithelial cells in the peripheral region of the prostate gland. Prostatic adenocarcinoma and benign prostatic hyperplasia are two common prostate diseases, which have a high rate of incidence in the aging human male population.
Approximately one out of every four males above the age of 55 suffers from a prostate disease of some form or another. Prostate cancer is the second most common cause of cancer related death in elderly men, with approximately 185,000 cases diagnosed and about 39,000 deaths reported annually in the United States.
Studies of the various substances synthesized and secreted by normal, benign and cancerous prostates carried out in order to gain an understanding of the pathogenesis of the various prostate diseases reveal that certain of these substances may be used as immunohistochemical tumor markers in the diagnosis of prostate disease. The three predominant proteins or polypeptides secreted by a normal prostate gland are: (1) Prostatic Acid Phosphatase (PAP); (2) Prostate Specific Antigen (PSA); and, (3) Prostate Secretory Protein of 94 amino acids (PSP94), which is also known as Prostatic Inhibin Peptide (PIP), Human Seminal Plasma Inhibin (HSPI), or β-microseminoprotein (β-MSP), and which is hereinafter referred to as PSP94.
PSP94 is a simple non-glycosylated cysteine-rich protein, and constitutes one of three predominant proteins found in human seminal fluid along with Prostate Specific Antigen (PSA) and Prostate Acid Phosphatase (PAP). PSP94 has a molecular weight of 10.7 kDa, and the complete amino acid sequence of this protein has already been determined. The cDNA and gene for PSP94 have been cloned and characterized (Ulvsback, et al., Biochem. Biophys. Res. Comm., 164:1310, 1989; Green, et al., Biochem. Biophys. Res. Comm., 167:1184, 1990). Immunochemical and in situ hybridization techniques have shown that PSP94 is located predominantly in prostate epithelial cells. It is also present, however, in a variety of other secretory epithelial cells (Weiber, et al., Am. J. Pathol., 137:593, 1990). PSP94 has been shown to be expressed in prostate adenocarcinoma cell line, LNCap (Yang, et al., J. Urol., 160:2240, 1998). As well, an inhibitory effect of exogenous PSP94 on tumor cell growth has been observed both in vivo and in vitro (Garde, et al., Prostate, 22:225, 1993; Lokeshwar, et al., Cancer Res., 53:4855, 1993), suggesting that PSP94 could be a negative regulator for prostate carcinoma growth via interaction with cognate receptors on tumor cells.
Native PSP94 has been shown to have a therapeutic effect in the treatment of hormone refractory prostate cancer (and potentially other prostate indications). For example, PSP94 expression within prostate cancer is known to decrease as tumor grade and agressivity increases. Tumor PSP94 expression is stimulated upon anti-androgen treatment, particularly in high grade tumors. U.S. Pat. No. 5,428,011 (Sheth A. R. et al., issued 1995-06-27), incorporated herein by reference, describes pharmaceutical preparations comprising native PSP94 used in the in-vitro and in-vivo inhibition of prostate, gastrointestinal and breast tumor growth. These pharmaceutical preparations include either native PSP94 alone or a mixture of native PSP94 and an anticancer drug such as, for example, mitomycin, idalubicin, cisplatin, 5-fluorouracil, methotrexate, adriamycin and daunomycin. In addition, the therapeutic effect of recombinant human PSP94 (rhuPSP94) and polypeptide analogues such as PCK3145 has been described in Canadian Patent Application No.: 2,359,650 (incorporated herein by reference).
Immunohistochemical studies and investigations at the level of mRNA have shown that the prostate is a major source of PSP94. PSP94 is involved in the feedback control of, and acts to suppress secretion of, circulating follicle-stimulating hormone (FSH) both in-vitro and in-vivo in adult male rats. PSP94 acts both at the pituitary as well as at the prostate site since both are provided with receptor sites for PSP94. PSP94 has been demonstrated to suppress the biosynthesis and release of FSH from the rat pituitary as well as to possibly affect the synthesis/secretion of an FSH-like peptide by the prostate. These findings suggest that the effects of PSP94 on tumor growth in vivo, could be attributed to the reduction in serum FSH levels.
Recently, it has been shown that PSP94 concentrations in serum of patients with BPH or CaP are significantly higher than normal. The highest serum concentration of PSP94 observed in normal men is approximatly 40 ng/ml, while in men with either BPH or CaP, serum concentrations of PSP94 have been observed up to 400 ng/ml.
In the serum, PSP94 occurs as a free (unbound) form or bound form associated with a carrier protein(s) of unknown identity. PSP94 in its bound form (state) has been quantified in the blood of prostate cancer patients and these measurements have been analyzed for their utility as prognostic evaluation (Bauman, G. S., et al., The Prostate J. 2:94-101, 2000; Xuan, J. W. U.S. Pat. No. 6,107,103; Wu, D. et al., J. Cell. Biochem. 76:71-83, 1999). It was suggested that measurements of the free and bound forms of PSP94 are likely to have a greater clinical relevance in several areas of prostate cancer than measurements of the free form alone. In addition, it was demonstrated that measurements of both forms of PSP94 allows an accurate prediction of relapse free interval in post-radiotherapy prostate cancer. However current assay for PSP94 measurement, such as the one described in U.S. Pat. No. 6,107,103 rely on a purification step for separating bound and free forms of the protein and therefore lack the simplicity necessary for a useful and efficient commercial assay.